Inlet header duct design features

ABSTRACT

A header duct and method of forming a header duct includes an inlet portion having a planar inlet, an outlet portion have a plurality of planar outlets, and a transition portion extending continuously from the inlet portion to the outlet portion. The transition portion has a bend and internal topography defining a non-monotonic cross-sectional area distribution between the inlet and outlet portions. The transition portion can further include a bulbous region extending in a lateral direction of the duct and a protrusion located along an inside radius of the bend.

BACKGROUND

The present invention relates to header ducts and, more particularly, tointernal topography of header ducts.

A header duct is a component shaped to distribute fluid from a source toa component attached to the header duct outlet. In some instances, theheader duct forms a manifold whereby fluid from a single source isdistributed among multiple outlets.

For example, FIG. 1A depicts prior art duct 10 that distributes fluidreceived through inlet 12 to first outlet 14 a and second outlet 14 b.Duct 10 includes inlet portion 16, transition portion 18, and outletportion 20. Inlet portion 16 extends from inlet 12 to transition portion18, and outlet portion 20 extends from transition portion 18 to firstand second outlets 14 a, 14 b. Transition portion 18 extends betweeninlet portion 16 and outlet portion 20 and is encompassed by bend 22,which permits an inlet plane containing inlet 12 to be angularly offsetwith respect to an outlet plane containing first outlet 14 a and secondoutlet 14 b. Furthermore, transition portion 18 has walls forming adistribution of cross-sectional areas that transition from a circularcross-sectional area that is continuous with inlet portion 16 to arectangular cross-sectional area that is continuous with outlet portion20.

FIG. 1B is a cross-sectional view of duct 10 taken along line 1B-1B inFIG. 1A in which line 1B-1B is coincident with center point 24 of inlet12. FIGS. 1C, 1D, and 1E are additional cross-sectional views takenalong lines 1C-1C, 1D-1D, and 1E-1E shown in FIG. 1B, respectively. Asgenerally shown by FIGS. 1B, 1C, 1D and 1E, transition portion 18 haswalls that are generally characterized by a simple, monotonic transitionbetween the circular cross-section of inlet 12 to the rectangularcross-section of outlet portion 20. Headers such as duct 10 are designedusing computer-aided-design (CAD) or a CAD-driven process in whichdesigners are primarily concerned with the physical constraints of duct10.

While duct 10 provides outlets 14 a and 14 b with fluid from inlet 12,headers designed with such CAD-driven processes fail to consider thefluid flow dynamics within duct 10 and result in unnecessarily highpressure loss through the duct due to flow separation regions, whichcreate a region of turbulent flow and effectively reduce thecross-sectional area of duct 10 near the separation region. Forinstance, as shown in FIG. 1B, flow separation region 26 results frombend 28 along outside radius duct wall 30, and flow separation region 27region results from bend 28 along inside radius duct wall 31.Consequently, flow lines 32 a, 32 b, and 32 c are diverted away fromregions 26 and 27, increasing the pressure loss and reducing flowuniformity through duct 10.

Increased pressure loss and reduced flow uniformity decrease performanceof components (e.g., one or more heat exchangers) which utilize fluiddelivered through first outlet 14 a and second outlet 14 b. The totalpressure loss through a system must not exceed the driving pressure bysome margin in order to achieve a design flow rate through the system.For example, header duct 10 may supply one or more heat exchangersconnected to first outlet 14 a and second outlet 14 b. Increasedpressure loss in header duct 10 limits the allowable pressure lossthrough the heat exchangers and, thus, limits the overall size orpassage geometry of the heat exchangers. Moreover, non-uniform flowdistributions through duct 10 concentrate flow through some passages ofthe heat exchanger and reduce flow through other heat exchangerpassages, thereby reducing the efficiency of the heat exchanger as wellas creating unnecessary pressure losses due to the concentrated flowpassages.

Accordingly, because duct manufactures continue to seek improved headerduct performance, a need exists for a header duct that furthereliminates or reduces pressure losses due to flow separation andimproves flow uniformity.

SUMMARY

A header duct includes an inlet portion having a planar inlet, an outletportion having multiple planar outlets, and a transition portionextending continuously from the inlet portion to the outlet portion anddefining a bend, making the outlets non-parallel with the inlet. Thetransition portion further includes internal topography defining anon-monotonic cross-sectional area distribution between the inlet andoutlet portions.

In a further embodiment of the header duct, the internal topography ofthe transition portion may define a bulbous, intermediate region and aprotrusion along an inside radius of the bend. The bulbous region has alarger cross-sectional area than a cross-sectional area of the inletmeasured along a first intermediate plane parallel to and offset fromthe inlet. The bulbous region further includes a convex curvatureadjacent the inlet portion that smoothly transitions to a concavecurvature within the bulbous region along a second intermediate planeperpendicular to the first intermediate plane and intersecting theinlet. Lateral walls of the bulbous region further include a concavecurvature that converges towards a lateral dimension of the outlets.

A method of forming a header duct includes forming an inlet portion thatextends from a circular inlet, forming an outlet portion with aplurality of rectangular outlets, and forming a transition portionjoining the inlet portion to the outlet portion. Forming the transitionportion includes forming internal topography that defines anon-monotonic cross-sectional area distribution between the inletportion and the outlet portion. The method can further include forming abulbous region defined by the internal topography that extends laterallyaway from a plane intersecting a center point of the inlet and extendingperpendicularly away from the inlet along a longitudinal direction ofthe outlets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an isometric view of a prior art header duct having a singleinlet and multiple outlets.

FIG. 1B is a cross-sectional view of the prior art duct depicted in FIG.1A taken through an inlet center point.

FIG. 1C is a cross-sectional view of the prior art duct depicted in FIG.1A taken along line 1C-1C and intersecting the duct inlet.

FIG. 1D is a cross-section view of the prior art duct depicted in FIG.1A taken along line 1D-1D and intersecting a first duct outlet.

FIG. 1E is a cross-section view of the prior art duct depicted in FIG.1A taken along line 1E-1E and intersecting a second duct outlet.

FIG. 2A is an isometric view of a header duct having features forreducing or eliminating flow separation and pressure loss as well asimproving flow uniformity.

FIG. 2B is a cross-sectional view of the header duct of FIG. 2A takenalong line 2B-2B.

FIG. 2C is a cross-sectional view of the header duct of FIG. 2A takenalong line 2C-2C showing a protrusion positioned along an inside bendradius and additional internal topography of header duct.

FIG. 2D is a cross-sectional view of the header duct of FIG. 2A takenalong line 2D-2D showing a bulbous region within a transition portion ofthe header duct.

FIG. 2E is an isometric view of the header duct of FIG. 2A showing theeffective bend radius resulting from the bulbous region depicted by FIG.2D.

DETAILED DESCRIPTION

FIG. 2A is an isometric view of header duct 100 extending from inlet 112to first and second outlets 114 a and 114 b. Duct 100 includes inletportion 116 extending from inlet 112 to transition portion 118 andoutlet portion 120 extending from transition portion 118 to outlets 114a and 114 b. Inlet 112 is contained within plane P1 and has a circularcross-sectional area. Outlets 114 a and 114 b are contained within planeP2 and have rectangular cross-sectional areas in which a longitudinaldirection of outlets 114 a and 114 b extends away from plane P1 along alengthwise dimension of outlets 114 a and 114 b. Accordingly, headerduct 100 includes bend 122, which as shown in FIG. 2A, facilitates a90-degree angular change between plane P1 of inlet 112 and plane P2 ofoutlets 114 a and 114 b. However, even though FIG. 2A depicts a90-degree bend, bend 122 can have any angular change measured betweenplanes P1 and P2 that is greater than 0 degrees and less than or equalto 90 degrees.

In addition to being angularly offset, outlets 114 a and 114 b can belaterally offset from inlet 112 as depicted in FIG. 2A and described inreference to planes P3 and P4 as follows. Inlet 112 includes centerpoint 124 located at the geometric center of inlet 112, and outlets 114a and 114 b have center points 126 a and 126 b, each located at thegeometric center of the respective outlets 114 a and 114 b. Plane P3passes through inlet center point 124 and extends perpendicularly frominlet 112 and plane P1. Plane P4 passes through outlet center points 126a and 126 b and extends perpendicularly from plane P3 as well as outlets114 a and 114 b. The lateral offset of outlets 114 a and 114 b frominlet 112 results in plane P4 extending parallel to and offset fromplane P3. In other embodiments of duct 100, inlet center point 124 iscoplanar with outlet center points 126 a and 126 b. As such, duct 100can be configured without a lateral offset between inlet 112 and outlets114 a and 114 b.

Transition portion 118 encompasses bend 122 and includes portions ofduct 100 that transition from a constant cross-sectional shape of inletportion 116 to a constant cross-sectional shape of outlet port 120 thatis different than the inlet portion 118 to form a continuous transitionfrom inlet portion 116 to outlet portion 120. While the cross-sectionalshapes of inlet portion 116 and outlet portion 120 are constant, inletportion 116 and outlet portion 120 may have converging or divergingwalls that increase or decrease the cross-sectional area of inletportion 116 and outlet portion 120.

Internal topography 128 of transition portion 118 (see FIGS. 2B, 2C and2D) defines a cross-sectional area distribution that is non-monotonic.In particular, transition region 118 includes at least one of bulbousintermediate region 130 and protrusion 132 that extends into an interiorof duct 100. Embodiments with bulbous region 130 have walls that extendlaterally away from plane P3 within an intermediate region of transitionportion 118. Protrusion 132 is located on an inside radius of bend 122and is between inlet portion 116 and outlet portion 120.

FIG. 2B is a cross-sectional view of header duct 100 taken along line2B-2B formed by the intersection between planes P1 and P3. Protrusion132 is continuous with and tangent to walls of inlet and outlet portions116 and 120, which is shown relative to a constant radius bend (shown asdashed line 134). When viewed in plane P3, protrusion 132 extends inwardfrom inside radius 122 a of bend 122, inside radius 122 a having asmaller turn radius than outside radius 122 b of bend 122. Accordingly,protrusion 132 extends further into an interior of duct 100 that aconstant radius bend 134 and forms convex curvature 132 a proximateinlet portion 116 that transitions to concave curvature 132 b proximateoutlet portion 120. The transition from convex curvature 132 a toconcave curvature 132 b occurs along a direction of flow from inlet 112to outlets 114 a and 114 b.

Additionally, inlet portion 116 can have walls defining a constantcross-sectional area distribution or, as shown in FIG. 2B, walls ofinlet portion 116 can diverge along a direction extending away frominlet 112 towards transition 118. While FIG. 2B shows diverging inletwalls as viewed along plane P3, walls of inlet portion 116 can also bediverging in a laterally-oriented plane as necessary for inlet portion116 to be continuous with bulbous region 130 of transition portion 118.

FIG. 2C is an isometric sectional view of header duct 100 taken alongline 2C-2C that is parallel to plane P2 and shows an additional view ofprotrusion 132 formed by internal topography 128. Along a lateraldirection extending away from plane P3, protrusion 132 forms convexcurvature 132 c disposed between concave curvatures 132 d and 132 e ordepressions. In some embodiments, convex curvature 132 c is centrallydisposed between convex curvatures 132 d and 132 e, being bisected byplane P3. Extending away from inlet 112 along the sectional plane ofFIG. 2C, internal topography transitions from concave curvatures 132 dand 132 e to convex curvatures 132 f and 132 g, respectively, beforejoining walls of outlet portion 120. The curvature distribution ofprotrusion 132 depicted by FIG. 2C is representative of othercross-sectional views taken parallel to section 2C-2C and offset towardsor away from outlets 114 a and 114 b, albeit with a higher or lesserdegree of curvature. In particular, as internal topography 128 extendsfrom section 2C-2C towards outlets 114 a and 114 b, the radii ofcurvature for curvatures 132 c, 132 d, and 132 e increase and approachthe curvature of outlet portion 120.

Protrusion 132 extends into a region that would form a flow separationregion (e.g., flow separation region 27 associated with duct 10 shown inFIG. 1B) if duct 100 where to be formed with constant radius bend 134.However, unlike the prior art ducts, protrusion 132 closely follows astreamline of fluid flowing from inlet 112 to outlets 114 a and 114 b,and, in particular, closely follows a streamline of a portion of fluidflowing to outlet 114 a, which is disposed closer to bend 122 thanoutlet 114 b. Therefore, duct 100 configured with protrusion 132 reducesor eliminates a region of flow separation proximate inside bend radius122 a and thereby reduces pressure drop through duct 100.

Moreover, FIGS. 2B and 2C depict protrusion 132 as being integrallyformed, or formed at the same time as transition portion 118 and as asingle piece. However, protrusion 132 may also be formed as a separate,discrete piece and joined later to transition portion 118. In someembodiments, protrusion 132 may be formed from sheet metal, which can bewelded, brazed, or joined using some other suitable mechanical means.For instance, protrusion 132 can have pre-formed holes that correspondto a pattern of mating holes formed through a wall of transition portion118. After aligning the holes of protrusion 132 with the holes oftransition portion 118, rivets secured through the hole patterns can beused to attach protrusion 132 to transition portion 118. In otherembodiments, protrusion 132 can be formed using an additivemanufacturing process in lieu of sheet metal.

FIG. 2D is an isometric sectional view of header duct 100 taken alongline 2D-2D, which intersects inlet 112 and is parallel to outlets 114 aand 114 b. FIG. 2D depicts bulbous region 130 within an intermediateregion of transition portion 118 in which bulbous region 130 is definedby internal topography 128 that extends laterally away from plane P3.Within the FIG. 2D sectional plane and in a direction extending awayfrom inlet portion 116 and towards transition portion 118, bulbousregion 130 includes convex curvatures 130 a and 130 b on opposinglateral sides of transition portion 118 that transition to concavecurvatures 130 c and 130 d, respectively. Extending further away frominlet 112, concave curvatures 130 c and 130 d transition to convexcurvatures 130 e and 130 f, respectively. Laterally opposing convexcurvatures 130 e and 130 f are joined by concave curvature 130 g.Bulbous region 130 creates an intermediate region in which across-sectional area taken through bulbous region 130 is larger than across-sectional area of inlet 112 in which the cross-sectional area ofbulbous region 130 is measured within intermediate plane P5. Plane P5intersects bulbous region 130 and is parallel to and offset from planeP1 containing inlet 112 such that plane P5 extends laterally betweenconcave curvatures 130 c and 130 d. In some embodiments, maximum lateraldimension M of duct 100 is within plane P5.

The cross-sectional view of FIG. 2D is representative of features ofbulbous region 130 taken through other sectional views parallel to andoffset from sectional view FIG. 2D. Views taken parallel to and offsettowards outlets 114 a and 114 ba approach the curvature of outletportion 120. In some embodiments, this trend produces lateral sides ofbulbous region 130 that converge towards a lateral dimension of outlets114 a and 114 b. Views taken parallel to and offset away from outlets114 a, 114 b have curvature profiles in which radii of curvatureincrease until opposing lateral sides join at an end of duct 100opposite outlets 114 a and 114 b.

FIG. 2E depicts a second isometric view of header duct 100 in which aneffective bend radius R is increased with the inclusion of bulbousregion 130. As shown in FIG. 2E, bend radius R is a three-dimensionalcurve that extends laterally away from plane P3 while curving towardsoutlets 114 a and 114 b. Radius R is larger than a bend radius of duct10 and, thus, contributes to reducing or eliminating a flow separationalong an inside bend radius of bend 122 (e.g., flow separation region27). Moreover, bulbous region 130 permits fluid flow bound for outlet114 a to turn more easily through bend 122, resulting in more uniformflow distribution through outlets 114 a and 114 b.

Discussion of Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

The header duct for suppling a fluid to one or more heat exchangersaccording to an exemplary embodiment of this disclosure, among otherpossible things includes an inlet portion having a planar inlet, anoutlet portion having first and second planar outlets, and a transitionportion extending from the inlet portion to the outlet portion thatdefines a bend such that first and second outlets are non-parallel tothe inlet. The transition portion is continuous with the inlet andoutlet portions and includes internal topography defining anon-monotonic cross-sectional area distribution between the inlet andoutlet portions.

The header duct of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the forgoing header duct can further include afirst plane and a second plane that is parallel to and offset to thefirst plane in which the first plane contains a center point of theplanar inlet that extends perpendicularly to the planar inlet and inwhich the second plane contains center points of the first and secondoutlets and extends parallel to a longitudinal dimension of the firstand second outlets.

A further embodiment of any of the foregoing header ducts, wherein theinternal topography can define a protrusion positioned between twodepressions disposed on the inside corner of the bend adjacent the inletportion.

A further embodiment of any of the foregoing header ducts that include aprotrusion, wherein the protrusion can be defined by a convex curvature.

A further embodiment of any of the foregoing header ducts that include aprotrusion, wherein the depressions can be defined by a concavecurvature when viewed in a cross section intersecting the protrusion andextending perpendicularly to the planar inlet.

A further embodiment of any of the foregoing header ducts, wherein theinternal topography can define an intermediate region with a largercross-sectional area than a cross-sectional area of the planar inlet.

A further embodiment of any of the foregoing header ducts that includean intermediate region, wherein the cross-section of the intermediateregion can be defined within a first intermediate plane intersecting theintermediate region that is parallel to and offset from the planarinlet.

A further embodiment of any of the foregoing header ducts that includean intermediate region having a cross-sectional area defined within thefirst intermediate plane, wherein the internal topography can define aconvex curvature adjacent the inlet portion that transitions to aconcave curvature along a second intermediate plane perpendicular to thefirst intermediate plane and intersecting the planar inlet.

A further embodiment of any of the foregoing header ducts that includean intermediate region, wherein the intermediate region can have amaximum lateral dimension that is coplanar with a center pointy of across-sectional area of the inlet that can be measured parallel to theplanar inlet, the first planar outlet, and the second planar outlet.

A further embodiment of any of the foregoing header ducts, wherein theinternal topography can define lateral walls that have a concavecurvature that converge towards a lateral dimension of the first andsecond planar outlets.

A further embodiment of any of the foregoing header ducts that have anintermediate region with a cross-sectional area defined within the firstintermediate plane and a curvature defined along the second intermediateplane, wherein the internal topography transitions from the concavecurvature at the first intermediate plane to a second convex curvaturein a direction extending away from the planar inlet along the secondintermediate plane.

A further embodiment of any of the foregoing header ducts, wherein theinternal topography can include a laterally-extending bulbous regionthat increases an effective radius of the bend within the transitionportion.

A further embodiment of any of the foregoing header ducts, wherein wallsof the inlet portion can diverge from the planar inlet to the transitionportion.

A further embodiment of any of the foregoing header ducts that include aprotrusion, wherein the protrusion can be a discrete component attachedto the transition duct.

A method of forming a header duct for suppling a fluid to one or moreheat exchangers according to an exemplary embodiment of this disclosure,among other possible steps includes: 1) forming an inlet portion thatextends from a planar inlet, 2) forming an outlet portion with aplurality of planar outlets, 3) forming a transition portion joining theinlet portion to the outlet portion, and 4) forming a bulbous regiondefined by internal topography of the transition portion. The transitionportion defines a non-monotonic cross-sectional area distribution thattransitions from the inlet portion to the outlet portion. The bulbousregion extends laterally away from a plane intersecting a center pointof the inlet and extending perpendicularly away from the inlet along alongitudinal direction of the outlets.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingsteps:

A further embodiment of the foregoing method can include forming aprotrusion along an inside radius of a bend between the inlet portionand the outlet portion in which the bend defines an angle between theplanar inlet and the planar outlets.

A further embodiment of any of the foregoing methods, wherein formingthe outlet portion can further include offsetting the plurality ofoutlets in a lateral direction away from the plane.

A further embodiment of any of the foregoing methods, wherein formingthe bulbous region can include forming lateral sides of the transitionregion that have a concave curvature that converges towards theplurality of outlets.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A header duct for supplying a fluid to one or more components, theheader duct comprising: an inlet portion having a planar inlet; anoutlet portion having first and second planar outlets that arenon-parallel to the inlet; and a transition portion extending from theinlet portion to the outlet portion and defining a bend, wherein thetransition portion is continuous with the inlet and outlet portions, andwherein the transition portion has an internal topography defining anon-monotonic cross-sectional area distribution between the inlet andoutlet portions.
 2. The header duct of claim 1, wherein a first planecontains a center point of the inlet and extends perpendicularly to theplanar inlet, and wherein a second plane contains center points of thefirst and second outlets and extends parallel to a longitudinaldimension of the first and second outlets, and wherein the first planeis parallel to and offset from the second plane.
 3. The header of claim2, wherein the inlet has a circular cross-sectional area, and whereineach of the first and second outlets has a rectangular cross-sectionalarea.
 4. The header of claim 1, wherein the internal topographycomprises: a protrusion positioned between two depressions and disposedon the inside corner of the bend adjacent to the inlet portion, whereinthe protrusion is defined by a convex curvature and the depressions aredefined by a concave curvature when viewed in a cross sectionintersecting the protrusion and extending perpendicularly to the planarinlet.
 5. The header of claim 1, wherein the internal topographycomprises: an intermediate region with a larger cross-sectional areathan a cross-sectional area of the planar inlet, wherein: thecross-sectional area of the intermediate region is defined within afirst intermediate plane intersecting the intermediate region that isparallel to and offset from the planar inlet; and the internaltopography defines a convex curvature adjacent the inlet portion thatsmoothly transitions to a concave curvature along a second intermediateplane perpendicular to the first intermediate plane and intersecting theplanar inlet.
 6. The header of claim 5, wherein the intermediate regionhas a maximum lateral dimension that is coplanar with a center point ofa cross-sectional area of the inlet, and wherein the maximum lateraldimension is measured parallel to the planar inlet, the first planaroutlet, and the second planar outlet.
 7. The header of claim 5, whereinthe internal topography includes lateral walls having a concavecurvature that converges towards a lateral dimension of the first andsecond planar outlets.
 8. The header of claim 5, wherein theintermediate region of the internal topography transitions from theconcave curvature at the first intermediate plane to a second convexcurvature in a direction extending away from the planar inlet along thesecond intermediate plane.
 9. The header of claim 1, wherein theinternal topography includes a laterally-extending bulbous region thatincreases an effective radius of the bend within the transition portion.10. The header of claim 1, wherein walls of the inlet portion divergefrom the planar inlet to the transition portion.
 11. The header of claim5, wherein the protrusion is a discrete component attached to thetransition duct.
 12. A header duct for supplying a fluid to one or morecomponents, the header duct comprising: an inlet portion having a planarinlet; an outlet portion having first and second planar outlets that arenon-parallel to the inlet; and a transition portion extending from theinlet portion to the outlet portion and defining a bend, wherein thetransition portion is continuous with the inlet and outlet portion, andwherein the transition portion has an internal topography defining anon-monotonic cross-sectional area distribution between the inlet andoutlet portions, and wherein the internal topography comprises: anintermediate region with a larger cross-sectional area than across-sectional area of the planar inlet, wherein: the cross-sectionalarea of the intermediate region is defined within a first intermediateplane intersecting the intermediate region that is parallel to andoffset from the planar inlet; and the internal topography defines aconvex curvature adjacent the inlet portion that transitions to aconcave curvature within the intermediate region along a secondintermediate plane perpendicular to the first intermediate plane andintersecting the planar inlet; a protrusion positioned between twodepressions and disposed on the inside corner of the bend adjacent tothe inlet portion, wherein the protrusion is defined by a convexcurvature and the depressions are defined by a concave curvature whenviewed in a cross section perpendicular to the planar inlet thatintersects the protrusion; and lateral walls that having a concavecurvature that converge towards a lateral dimension of the first andsecond planar outlets.
 13. The header duct of claim 12, wherein a firstplane containing a center point of the inlet and extendingperpendicularly to the planar inlet is parallel to and offset from asecond plane containing center points of the first and second outletsand extending parallel to a longitudinal dimension of the first andsecond outlets.
 14. The header of claim 13, wherein the inlet has acircular cross-sectional area, and wherein each of the first and secondoutlets has a rectangular cross-sectional area.
 15. The header of claim12, wherein the intermediate region has a maximum lateral dimensionmeasured parallel to the planar inlet and the first and second planaroutlets is coplanar with a center point of a cross-sectional area of theinlet.
 16. The header of claim 12, wherein walls of the inlet portiondiverge from the planar inlet to the transition portion.
 17. A method offorming a header duct, the method comprising: forming an inlet portionthat extends from a planar inlet; forming an outlet portion with aplurality of planar outlets; forming a transition portion joining theinlet portion to the outlet portion that defines a non-monotoniccross-sectional area distribution that transitions from the inletportion to the outlet portion; and forming a bulbous region defined byinternal topography of the transition portion, wherein the bulbousregion extends laterally away from a plane, and wherein the planeintersects a center point of the inlet and extends perpendicularly awayfrom the inlet along a longitudinal direction of the outlets.
 18. Themethod of claim 17, and further comprising: forming a protrusion alongan inside radius of a bend between the inlet portion and the outletportion in which the bend defines an angle between the planar inlet andthe planar outlets.
 19. The method of claim 18, wherein forming theoutlet portion includes: offsetting the plurality of planar outlets in alaterally direction away from the plane.
 20. The method of claim 17,wherein forming the bulbous region includes: forming lateral sides ofthe transition region that have a concave curvature that convergestowards the plurality of planar outlets.